JPS62235737A - Formation of insulating film on semiconductor sub-strate - Google Patents

Abstract

PURPOSE:To form an insulating film with excellent thermal and moisture resistance, easily flattened thick film-forming property without using any vacuumizing system by a method wherein a semiconductor substrate is coated with a coating agent mixed with specified silane compound and specified zirconium compound to be hardened by heat-treat-ment and then a resist mask formed on a hardened film is removed after etching process. CONSTITUTION:A semiconductor substrate 1 with lower interconnections 2 formed thereon is spin-coated with a coating agent mixed with 10 weight % of zirconium tetra-n-butoxide and 60 weight 5 of isopropylalcohol at an r.p.m. attaining to specified film thickness to be hardened by heat-treatment in the air. Next, after forming a resist film on a hardened film 3, the hardened film 3 is etched by RIE process using C2F6 gas as well as a resist pattern 4 formed by photolithography as a mask to form a connecting hole 7 between upper and lower interconnections. Finally, the resist pattern 4 is removed by plasmaetching process and then an upper layer interconnection 5 is formed by evaporating a metallic layer as the upper layer interconnection 5 on overall surface to be dryetched.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming an insulating film used in semiconductor integrated circuits and the like. Specifically, the present invention relates to a method for forming an interlayer insulating film, a protective film, a planarization film, etc. used in a multilayer wiring structure.

Prior Art The prior art will be explained using FIG. 4, taking a multilayer wiring structure as an example.

Lower layer wiring 2 is formed on semiconductor substrate 1 on which predetermined elements are formed. An S102 film 6, which is an interlayer insulating film, is formed on the lower layer wiring 2 using a vapor phase growth method such as a CVD method (
Figure 4 (to)). A resist 4 (see FIG. 4) is formed on the 5102 film 6 using a normal photolithography process, and using this as a mask, the Si02 film 6 is dry-etched to form upper and lower wiring connection holes. Finally, a wiring metal layer such as AI is deposited and dry etched to form a multilayer wiring structure as the upper layer wiring 6 (FIG. 4(Q)).

3' In the above-mentioned conventional method, since an insulating film formed by a vapor phase growth method is used as an interlayer insulating film, there are problems such as disconnection of the upper layer wiring due to the residual step of the underlying layer and short circuit between the upper and lower wiring due to poor coverage of the step.

To solve these problems, organic polymer resins and spin-on glass (product name: Merck & Co., Ltd.), which are excellent at flattening substrate steps, have been proposed, but organic polymer resins are less effective than inorganic insulating films. It has the disadvantage of poor heat resistance and moisture resistance,
Spin-on glass has the disadvantage that cracks occur when the film thickness is 0.3 μm or more. For this reason, forming methods such as etch-back are used to form the interlayer insulating film, but there are problems in that the steps are complicated and damage to the elements occurs.

Problems to be Solved by the Invention As described above, insulating films formed by vapor phase growth methods may cause residual step differences in the base layer, disconnections in upper layer interconnects in multilayer interconnect structures due to poor coverage, short circuits between upper and lower interconnects, etc. There are problems such as reduced reliability, and complicated processes. Further, organic polymer resins are excellent in flattening the substrate because they can form an insulating film by spin coating, but they have a problem in that they are inferior in heat resistance and moisture resistance compared to inorganic insulating films.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method using the general formula S l (OR
) 4 (wherein, R is a tetraalkoxysilane having 1 to 5 carbon atoms (D [indicating a hydrogen residue)], a hydrolyzate of the tetraalkoxysilane, and a partial polycondensate of the hydrolyzate. At least one silane compound selected from the group of Hydrolyzate of alkoxide.

and a step of applying a coating agent mixed with at least one zirconium compound selected from the group of partial polycondensates of the hydrolyzate, a step of curing the coating agent by heat treatment to form a cured film, Provided is a method for forming an insulating film on a semiconductor substrate, comprising the steps of forming a resist mask on the cured film and etching the cured film, and removing the 6'-diresist mask. It is something to do.

Function As described above, since the coating agent used in the present invention is a liquid type, it can be formed by a method such as spin coating that does not use a vacuum system. In addition, its concentration is higher than that of conventional spin-on glass, and its viscosity is lower than that of organic polymer resins such as polyimide resin, so it is superior in flattening compared to conventional materials. Furthermore, it is possible to form a thick film of 1 μm or more, and after curing, it becomes an insulating film with excellent heat resistance and moisture resistance.

Furthermore, the coating agent used in the present invention can be cured in N2 or air at a low temperature of 80'C to 300C, and can be cured in a short processing time of several tens of minutes. Therefore, it is also effective in preventing stress migration in the wiring metal layer. In addition, since the same method as for the 51o2 film is used in the etching process, conventional equipment can be used, and the etching process for insulating films used in a multilayer structure with the S502 film, such as the etchback method, can be easily performed. Become.

Examples First, the coating agent used in the present invention will be explained.

Specific examples of the coating agent used in the present invention include coating agents obtained by mixing the following components (,) to (c).

(,) General formula 5t(OR)4 (wherein, R is 1 carbon number
~5 hydrocarbon residues are shown. ), a hydrolyzate of the tetraalkoxysilane, and 6 to 60 parts by weight of a partial polycondensate of the hydrolyzate, (b) general formula Z r (OR')4 (in the formula, R ′
represents a hydrocarbon residue having 1 to 6 carbon atoms. ) 3 to 30 parts by weight of at least one zirconium compound selected from the group of zirconium tetraalkoxide represented by zirconium tetraalkoxide, a hydrolyzate of the zirconium tetraalkoxide, and a partial polycondensate of the hydrolyzate, and <a> organic Solvent 20-90 parts by weight 7 parts ((a) + (b) + (a) -100
parts by weight).

The components (a) to (C) will be explained below.
' compound) Silane compound tetraalkoxysilane; S x (OR) 4 is
In the presence of water, it is hydrolyzed to form a hydrolyzate, and the hydrolyzate is polycondensed to form a partial polycondensate, which further increases in molecular weight and becomes a coating film, which is cured by heating, and the present invention In the composition, it acts as a binder together with the zirconium compound (b).

R in such tetraalkoxysilane is, for example, an alkyl group having 1 to 6 carbon atoms, such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, 5
Examples include ea-butyl group and tert-butyl group.

Specific examples of these tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, ftra-i-propoxysilane, tetra-n-butoxysilane, and tetra-5ea.
-butoxysilane, tetra-tert-butoxysilane, etc. These tetraalkoxysilanes can be used alone or in combination of two or more.

Furthermore, among these tetraalkoxysilanes, tetraethoxysilane is particularly preferred.

In addition, such tetraalkoxysilane partially liberates alcohol by hydrolysis, producing a corresponding hydrolyzate, and polycondensation of the hydroxyl substituent by producing silanol occurs in the presence of water, resulting in the formation of silanol. A partial polycondensate is produced, which is further polycondensed to produce a silica component which is a complete polycondensate.

Therefore, in the coating agent used in the present invention (
-) The silane compound includes, in addition to the above-mentioned tetraalkoxysilane, a hydrolyzate thereof and a partial polycondensate of the hydrolyzate. Such hydrolyzate and/or partial polycondensate may be produced from tetraalkoxysilane in the coating agent, and the hydrolyzate and/or partial polycondensate, For example, ethyl silicate 40 (Colcoat ■
(manufactured by) may be blended.

The proportion of the silane compound (a) in the coating agent is 6 to 60 parts by weight, preferably 20 to 40 parts by weight; if it is less than 6 parts by weight, the storage stability of the coating agent itself is good, but it cannot be used for coating. As a result, the adhesion of the resulting coating film becomes weaker, and the hardness does not improve sufficiently.
On the other hand, if it exceeds 60 parts by weight, the proportion of the zirconium compound becomes relatively small, and hydrolysis does not proceed in a short period of time, resulting in poor film-forming properties.

(b) Zirconium compound zirconium tetraalkoxide; Z r (OR'
) 4 is hydrolyzed in the presence of water to form a hydrolyzate (zirconium tetrahydroxide), and this hydrolyzate is polycondensed to produce a partial polycondensate, which further increases in molecular weight to form a coating film. It hardens by heating.

10'-diR' in such zirconium tetraalkoxide is, for example, a purkyl group having 1 to 5 carbon atoms, such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, 5ea-butyl group, etc. group, tert-butyl group, etc.

Specific examples of these zirconium tetraalkoxides include zirconium tetratoxide, zirconium tetraethoxide, zirconium tetrapropoxide, zirconium tetra-1-propoxide, zirconium tetra-n-butoxide, zirconium tetra-8&
)-butoxide, zirconium tetra-tert-butoxide, and the like.

These zirconium tetraalkoxides can be used alone or in combination of two or more.

Among these zirconium tetraalkoxides, zirconium tetra-n-butoxide is particularly preferred.

In addition, such zirconium tetraalkoxide liberates alcohol by rapidly hydrolyzing, producing the corresponding zirconium hydroxyl-11-pa-site, and polycondensation of the hydroxyl substituent occurs due to the formation of the hydroxide. A partial polycondensate of hydroxide is produced, which is further polycondensed to produce a zirconia component, which is a fully fed material.

Therefore, in the coating agent used in the present invention,
(b) The zirconium compound includes not only the above-mentioned zirconium tetraalkoxide but also its hydrolyzate and partial polycondensate of the hydrolyzate. Such hydrolyzate and/or partial polycondensate may be produced from zirconium tetraalkoxide in the coating agent, or may be blended in advance during preparation of the coating agent.

The proportion of the zirconium compound (b) in the coating agent is 3 to 30 parts by weight, preferably 8 to 20 parts by weight; less than 3 parts by weight is relatively small. Decomposition does not proceed, resulting in poor film-forming properties.On the other hand, if the amount exceeds 30 parts by weight, the storage stability of the resulting coating agent deteriorates due to the proportion of (b) zirconium compound being too high, and hydrolysis is too rapid, resulting in poor film-forming properties. Both of these are not desirable.

(c) Organic solvent The organic solvent is a concentration adjusting agent for the above-mentioned (a) silane compound and (b) zirconium compound, and further includes these (a)
, (b) is for controlling the hydrolysis of component.

Suitable examples of such organic solvents include alcohols, glycol derivatives, and low-boiling organic solvents having a boiling point of 120'C or less.

Among these, examples of the alcohols or glycol derivatives include ethylene glycol, which is a monohydric alcohol but also a dihydric alcohol, and its derivatives. Among these, monohydric alcohols include aliphatic alcohols having 1 to 8 carbon atoms. Preferably, specifically methanol,
Ethanol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, sea-butyl alcohol, tart-butyl alcohol, n-pendel alcohol, n-hexyl alcohol, 4-methyl-2-pentanol , 4-methyl-n-
Pentanol and the like can be mentioned, and examples of ethylene glycol or its derivatives include ethylene glycol, ethylene glycol mobutyl ether, and acetic acid ethylene glycol monoethyl ether. These alcohols and glycol derivatives are preferably i-propyl alcohol, s-butyl alcohol, n-propyl alcohol, n-butyl alcohol, acetic acid ethylene glycol monoethyl ether,
Al with ethylene glycol motubutyl ether.

In addition, as a low boiling point organic solvent with a boiling point of 120°C or less,
Examples include toluene, benzene, acetone, methyl ethyl ketone, cyclohexane, and tetrahydrofuran.

These organic solvents can be used alone or in combination of two or more.

In the coating agent used in the present invention, (C)
- The proportion of the organic solvent is from 20 to 90 parts by weight, preferably from 40 to 90 parts by weight.
If it is less than 20 parts by weight, the viscosity of the coating agent will increase too much or the storage stability will deteriorate;
If it exceeds 0 parts by weight, the storage stability of the coating agent itself will improve, but the solid content in the coating agent will decrease, making it impossible to achieve a thick coating film, and the rate of hydrolysis will decrease. This results in insufficient curing in a short period of time.

The coating agent used in the present invention may contain a filler in order to exhibit various functions such as heat resistance, thermal conductivity, and electrical resistance, and to exhibit further thickening.

Such fillers include, for example, inorganic pigments such as particulate, fibrous or feathered metal oxides or nitrides;
Furthermore, there are hydrolysates of metal alkoxides represented by M(OR2)n (M is a metal atom other than silicon or zirconium, R2 is an alkyl group, and n is an integer), and specifically, boron nitride, aluminum nitride, etc. , titanium oxide (T10
2), 16 = aluminum oxide (At203), chromium oxide (Cr2
o3), sillimite (At203.5iO2), synthetic mullite (3A1203.2 S102), mica, potassium titanate, silicon oxide, silicon carbide, silicon nitride, zirconia silicate, copper oxide, etc. However, the average major axis of these fillers is 0.01 to 100 μm, preferably 0.0 μm.
It is about 2 to 10 μm.

In addition, among these fillers, the average major axis is 0.02
Some become transparent when the thickness is less than μm.

For example, oxidation accompaniment, aluminum oxide, etc.

The proportion among such fillers is preferably up to 60 parts by weight, particularly preferably up to 50 parts by weight.

The coating agent used in the present invention is simply (,) to (C)
It can be prepared by mixing the components and the filler used if necessary, and in this case (c) may be aged (by refluxing).

As described above, since the coating agent used in the present invention is a liquid type, it can be formed by a method that does not use a vacuum system, such as spin coating. Also, its concentration is lower than that of conventional spin-on.
It has a higher concentration than glass and a lower viscosity than organic polymer resins such as polyimide resin, so it is better at flattening than conventional materials. Furthermore, it is possible to form a thick film of 1 μm or more, and after curing becomes an S102 film, it becomes an insulating film with excellent heat resistance and moisture resistance.

Furthermore, the coating agent used in the present invention can be cured in N2 or air at a low temperature of 80° C. to 300° C., and can be cured in a short processing time of several tens of minutes. Therefore, it is also effective in preventing stress migration in the wiring metal layer. In addition, although the etching process requires a slight increase in PIEpower compared to the SzO21 film, the same method as for the SiO2 film can be used, so conventional equipment can be used, and a multilayer structure with the 8102 film, such as the etchback method, can be used. The etching process becomes easier for the insulating film that has 17 layers.

(Example 1) A multilayer wiring structure using the present invention will be described with reference to FIG.

1 is a semiconductor substrate on which a semiconductor integrated circuit is built.

A coating agent obtained by mixing 30 parts by weight of tetraethoxysilane, 10 parts by weight of zirconium tetra-n-butoxide, and 60 parts by weight of isopropyl alcohol is applied onto a semiconductor substrate 1 on which a lower layer wiring 2 such as At is formed using a spinner. Coat at a rotation speed to achieve the desired film thickness using a
Heat treatment is performed for 30 minutes at 150°C for 30 minutes to harden the film.

A resist film is formed on the cured film 3, and a resist pattern 4 is formed using a normal photolithography process (FIG. 1A).
. Mask the resist pattern 4 and apply the cured film 3 to 02F.
Etching is performed by RIE using 6 gas to form upper and lower wiring connection holes (through holes) 7 (FIG. 1B). After the resist pattern 4 is removed by 02 plasma etching or fuming nitric acid or the like, a metal layer which will become the upper layer wiring is deposited on the entire surface and dry etched using the resist pattern to form the upper layer wiring 5 (FIG. 1C).

The cured film of the coating agent used in the present invention has excellent chemical resistance and is free from 02 frisma etching and film roughening caused by fuming nitric acid, which are disadvantages of organic insulating film materials. Furthermore, since the thermal loss starting temperature is as high as 80° C., it is stable even in heat treatment for Al sintering, and no cracks occur. The surface of the substrate after forming the thinned film has less steps and is excellent in flattening, as shown in Figure 1q.
As shown in Figure 2, there are no disconnections in the upper layer wiring due to the board level difference, or short circuits between the upper and lower wiring due to poor coverage.

The above method is not limited to two-layer wiring, but can also be applied to multi-layer wiring of three or more layers.

(Example 2) An etch-back method using the present invention will be explained using FIG. 2. S1 is grown on the semiconductor substrate 1 on which predetermined elements and lower layer wiring 2 are formed using a vapor phase growth method such as a CVD method.
02 film 6 with a thickness of 1 to 2 μm (FIG. 2A), the Si
A 19" coating agent is applied on the O2 film in the same manner as in Example 1 and hardened by heat treatment to flatten the surface (Fig. 2B). Two-layer insulation of SiO2 film 6 and cured film 3 The film is etched using isotropic etching until the desired thickness is reached and the surface is flattened (see Figure 2C).
). In the conventional method, an organic polymer such as a resist film is used as a flattening film on an insulating film, so after O plasma etching, S
Etching had to be performed under conditions where the etching speed of the iO2 film and the resist film were equal, which caused problems in confirming the etching end point and setting etching conditions. Etching can be performed all at once under different conditions, simplifying the process and improving reproducibility.

A similar application is to fill in poor coverage areas of an 8102 film formed on a fine pattern by vapor phase growth. SiO2 is deposited on the fine pattern using CVD method etc.
When the film is formed, a space 10 is created in the recess as shown in FIG. Therefore, during cleaning or wet etching, the solution tends to remain in the space, causing defects. Therefore, an insulating film is formed using the present invention on the insulating film formed by the vapor phase growth method to fill the spaces in the four parts. Since the coating agent used in the present invention is a liquid type, it is formed thicker on the recesses and thinner on the protrusions, and can fill the four spaces with almost no change in the film thickness on the protrusions.

Effects of the Invention As described above, since the coating agent used in the present invention is a liquid type, it can be formed by a method that does not use a vacuum system, such as spin coating. Also, its concentration is lower than that of conventional spin-on.
It has a higher concentration than glass and a lower viscosity than organic polymer resins such as polyimide resin, so it is better at flattening than conventional materials. Furthermore, it is possible to form a thick film of 1 μm or more, and after curing, it becomes an insulating film with excellent heat resistance and moisture resistance.

Further, the coating agent used in the present invention can be cured in N2 or air at a low temperature of 80 DEG C. to 300 DEG C., and can be cured in a short processing time of several tens of minutes. Therefore, it is possible to use the conventional equipment for stress reduction 21 purging of the wiring metal layer.
Insulating films used in a multilayer structure with two films facilitate the etching process.

As described above, according to the present invention, a flat and highly reliable insulating film can be formed by a simple method, which greatly contributes to the production of high-density semiconductor devices.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of the process steps of an embodiment of the present invention, Figure 3 is a cross-sectional view of a semiconductor substrate after the formation of a vapor phase grown SiO2 film, and Figure 4 is the formation of multilayer wiring by a conventional method. It is a process cross-sectional view of a method. 1... Semiconductor substrate, 2... Lower layer wiring,
3...Coating agent of the present invention, 4...
・Resist mask, 6... Upper layer wiring, 7...
...Through hole. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure tlLzFigure 3

Claims (1)

[Claims] A tetraalkoxysilane represented by the general formula Si(OR')_4 (in the formula, R represents a hydrocarbon residue having 1 to 5 carbon atoms) and the tetraalkoxysilane on which predetermined elements and wiring have been formed are At least one silane compound selected from the group of hydrolysates of alkoxysilanes and partial polycondensates of the hydrolysates; A coating agent prepared by mixing at least one zirconium compound selected from the group of zirconium tetraalkoxide represented by (representing a hydrogen residue), a hydrolyzate of the zirconium tetraalkoxide, and a partial polycondensate of the hydrolyzate. , a step of curing the coating agent by heat treatment to form a cured film, a step of forming a resist mask on the cured film and etching the cured film, and a step of removing the resist mask. Features: A method for forming an insulating film on a semiconductor substrate.